The Win64 builds of Thunderbird 60.0 are Not officially supported which is why they are not listed on https://www.thunderbird.net/thunderbird/all/ along with 32-bit version for Windows. The Win64 was not needed like 64-bit builds were needed for Mac and Linux.

Thunderbird changed it's build process to move it into line with the Firefox process. A side effect is a 64-bit (Win64) builds appearing in the release folders by accident since.

Win64 Releases of Thunderbird may not be officially supported until next year. So use that Win64 Thunderbird 60.0 and Beta builds at your own risk.

Approximately 5-10% of users have an add-on (other than Lightning). Unfortunately there is literally no mechanism to forewarn users that their add-ons may break in a future version. This has never been possible, but now of course the current state of code makes it more of a problem.

The version linked in that thread works for me with Thunderbird 64.0b1 in arch linux (64bit) - once Thunderbird had been upgraded to 64.0b1 I installed the xpi file from the addons menu, and restarted Thunderbird. Then closed and restarted again - calendar asked me to reauthorise the google calendar at that point, and from then all worked without further issue.

Well, I went ahead and installed it. Odd thing is the Lightning is version 6.6, but read this:"LightningIntegrated Calendaring & Scheduling for your Email clientMake Thunderbird or Seamonkey even more powerful with the fully integrated Lightning Calendar. Lightning allows you to organize your schedule, access remote calendars and much more. Try it today!

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=====================================================Lighting 4.0.5.2 for Thunderbird 38 is available here=====================================================

Lightning also supports older versions of Thunderbird like 24 or 31, please see the complete version history for details."